Cutting gear teeth: Slicing straight teeth is usually comparatively easier than trimming helical teeth. Equipment milling or gear hobbing can be used to cut tooth of spur and helical gears. In milling, only two simultaneous motions are wanted to cut the teeth of spur gears; nevertheless, three simultaneous motions are necessary for cutting the teeth of helical gear.
Impact load, vibration and noise: Since teeth of two mating spur gears will come in sudden contact, so they experience a shock or effect load. This also produces significant vibration and noise, which sometimes impose limit on maximum permissible speed of operation. On the contrary, gradual contact between 
mating teeth results a gradual load on one’s teeth and lower vibration and sound. Thus helical gears can be employed at higher speed without much problem.
Contact situation between mating teeth: Spur gears have straight teeth parallel to gear axis. Two mating gears are also installed in parallel shafts. Thus tooth of two mating spur gears come in sudden contact and the get in touch with is always a line of duration equals to teeth encounter width. On the contrary, helical gears have helical teeth plus they are mounted on parallel shafts. So teeth of two mating helical gears can be found in gradual get in touch with. Their engagement starts with a point and becomes a line and then gradually disengages as a spot. So contact length will not remain constant.
Orientation of driver and driven shafts: One fundamental advantage of equipment drive over other mechanical drives (like belt or chain drive) is the possibility to use for nonparallel shafts. However, various kinds gear are suitable for various orientations of driver and powered shafts. Both spur equipment and helical gears are overwhelmingly used for parallel shafts; whereas, bevel gears can be utilized for intersecting shafts and worm gear can be used for perpendicular nonintersecting shafts. There is a particular type of helical equipment, called crossed helical equipment, which can be employed for transmitting power between perpendicular shafts. This is very similar to worm equipment; however, crossed helical equipment cannot offer high velocity decrease. Typically, it is suitable for 1:1 to 1 1:2 acceleration ratio (as compared to 1:15 to at least one 1:100 in worm gear). Its application is also limited due to many limitations.